The present invention pertains to a device for displaying video, graphics, and other visual data to a user via a flat-panel display. More specifically, a device is provided for reducing the number of signals needed to drive a display, and consequently reducing the number of active drive components in a flat-panel display.
Flat-panel displays such as liquid crystal display (LCD) screens are used on computer systems, especially portable computer systems such as lap-top and hand-held computers. In addition, flat-panel displays are increasingly being employed for use as televisions or for other display purposes (e.g., video conferencing). Flat-panel displays are displays used for displaying computer and other analog and digital data, where the depth of the display is greatly reduced compared to traditional cathode ray tube (CRT) technologies. CRT displays use an electron beam to stimulate phosphor xe2x80x9cdotsxe2x80x9d on a glass screen into giving off light in a certain pattern to display data. Since the electron beam is located behind the screen and must xe2x80x9csweepxe2x80x9d across it, the display must occupy a certain depth behind the screen. Flat panel displays employ technologies such as light emitting diode (LED), thin film transistor (TFT) LCD, Organic Light Emitting Diode (OLED), plasma display panel (PDP), plasma addressed liquid crystal display (PALD), field emission display (FED), and light emitting polymer (LEP) to display computer data without the requirement of occupying the space behind the display to the extent necessary in CRT systems.
Computer data is displayed on display screens of computer monitors. A flat-panel display screen such as an LCD screen contains pixels made up of cells which are illuminated in patterns to form images (letters, numbers, pictures, and other graphics). The cell is the smallest physical unit which makes up a computer graphics image. On certain video display screens, such as LCD screens, each cell includes a transparent electrode that operates to apply current to liquid crystals to allow or prevent light from passing through the screen. In the case of color screens, each cell may include a color filter to assign a color value to that cell. Cells are assigned one of the three basic display colors: red, blue, or green.
A pixel is a picture element and, from the perspective of computer software that outputs display data, it is the smallest element of a graphics image. For color display screens, each pixel includes three cells, one of each of the basic display colors. By varying the luminance (brightness) of each cell, the pixel can be used to display a whole range of colors. The display data and commands output by a software program are processed by a display driver and output as graphics data to a graphics controller, which controls the display of each pixel on the screen. The number of pixels capable of being displayed by the fixed number of dots on a screen is the resolution of the screen.
The display data and commands output by a software program are processed by a display driver and output as graphics data to a graphics controller, which controls the display of each pixel on the screen. With each pixel comprised of three color elements, each pixel is driven by three signals. Therefore, each two by two pixel block is driven by twelve discrete values. This requires a significant number of active electronic components to drive the signals for all these pixel elements and is a major cost in the designing and building of a flat-panel display.
In the example of digital video data display, a flat-panel display system employing current technology sends compressed digital video data to a digital video decoder. The digital video decoder decodes the compressed digital video data into luminance (Y) and chrominance (Cb, Cr) data. This YCbCr data is then sent to a digital to analog converter (DAC) including color space conversion functionality, which converts it to analog RGB signals for the red, blue, and green cells of each pixel. This DAC employs a feature to convert digital luminance and chrominance values into analog RGB signals. The RGB signals applied to each cell control the brightness of the cell, and the combined brightness of each RGB cell creates the total color output and brightness for the relevant pixel. In systems such as this, each two-by-two block of pixels requires twelve signals to control it (three separate RGB signals for each pixel).
In the example of display of data output by the graphics portions of software programs, the data is generally output as RGB data. This data is temporarily stored in a frame buffer, and sent via a controller to the display, after conversion into analog signals by a DAC.
Flat-panel displays are generally designed to be thin, and are generally more expensive than traditional cathode ray tube (CRT) displays. Furthermore, in contrast to CRT displays, expanding the size of a flat-panel display requires adding additional components, which is also expensive. Reducing the number of signals required to control the display can save space and lead to significant cost savings by reducing the number of components required to control the display screen.
One embodiment of the present invention provides for a flat-panel display system including a flat-panel display screen including a plurality of pixels, a block of pixels including at least two of the plurality of pixels, a first drive circuit adapted to provide a luminance signal to each pixel in the block of pixels, a second drive circuit adapted to provide a first sub-sampled chrominance signal and a second sub-sampled chrominance signal to each block of pixels, at least one circuit adapted to latch the luminance and chrominance signals for each block, and at least one circuit adapted to generate a color display signal for a pixel from the luminance and chrominance signals sent to the pixel.